Adding first class Description field to SAMSequenceRecord

[lbergelson]

• The @sq DS header field was added to the 1.6 bam spec, this adds a getter and setter for it.
• We do not correctly support UTF-8 characters in description due to Htsjdk mangles unicode when writing sam files (and possibly bam/cram) #1202

Checklist

• Code compiles correctly
• New tests covering changes and new functionality
• All tests passing
• Extended the README / documentation, if necessary
• Is not backward compatible (breaks binary or source compatibility)

[codecov-io]

Codecov Report

Merging #1209 into master will increase coverage by 0.002%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##              master     #1209       +/-   ##
===============================================
+ Coverage     68.702%   68.704%   +0.002%     
- Complexity      8061      8063        +2     
===============================================
  Files            542       542               
  Lines          32711     32713        +2     
  Branches        5533      5533               
===============================================
+ Hits           22473     22475        +2     
  Misses          8038      8038               
  Partials        2200      2200

Impacted Files	Coverage Δ	Complexity Δ
...c/main/java/htsjdk/samtools/SAMSequenceRecord.java	71.429% <100%> (+0.697%)	36 <2> (+2)	⬆️

[jamesemery]

While I might contend that there are other first class attributes that don't have getters on SamSequenceRecord, those are independent of this being a useful change. 👍